Cu-doped mesoporous VOx-TiO2 in catalytic hydroxylation of benzene to phenol

Liquid phase hydroxylation of benzene to phenol with hydrogen peroxide over VOx-TiO2 catalyst samples with Cu as a second metal was investigated. A series of Cu/VOx-TiO2 (vanadium loading was 4.3%) catalysts were prepared within the range of Cu loading (0.29%–2.5%) and calcined at the temperatures of 350–650 °C. The catalyst samples were characterized by N2 adsorption-desorption, scanning electron microscopy, H2 temperature-programmed reduction, X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. After the addition of Cu, the Cu/VOx-TiO2 catalyst had more ordered mesoporous structure as compared with the VOx-TiO2 catalyst, and the vanadium was monodispersed on the TiO2 support. The presence of Cu2+ ions on the catalyst surface was shown by XPS measurements. These Cu2+ ions probably contributed to the dispersion of vanadium on the surface of the TiO2 support, and the more facile reduction of VOx. The Cu2+ ions also strengthened the thermostability of the Cu/VOx-TiO2 catalyst. The effects of some other variables (Cu loading, catalyst amount, and reaction temperature) on the catalytic performance were also investigated.

摘要将 Cu 作为第二金属, 制备了不同 Cu 掺杂量的和不同温度下焙烧的双金属改性的 Cu/VOx-TiO2 复合催化剂, 并用于液相苯直接羟基化制苯酚反应中. 固定钒的含量为 4.3%, 合成了一系列不同 Cu 掺杂量 (w = 0.29%–2.5%) 的催化剂, 并在不同的温度下 (350–650 °C) 进行了焙烧. 利用 X 射线衍射、N2 吸附-脱附、扫描电镜、透射电镜、H2 程序升温还原以及 X 射线光电子能谱对催化剂进行了表征. 结果表明, 加入 Cu 后催化剂仍保持有序的介孔结构, 并且有效地促进了 VOx 物种在载体 TiO2 上的分散和 VOx 物种的还原, 同时提高了催化剂的热稳定性, 其中 Cu 以 +2 价的形态存在于催化剂中. 另外, 考察了催化剂用量, 反应温度等对苯羟基化反应性能的影响.

Graphical AbstractIncorporation of Cu additives into a VOx/TiO2 catalyst improved the reducibility of VOx species, while Cu helped the monodispersion of VOx species on the TiO2 support surface.Figure optionsDownload full-size imageDownload as PowerPoint slide